I'm on the side of "hold off on judging the mother because we don't know enough about her yet". The father might just be garbage enough that she can't do enough to support the kids, and she may have not known why her son left (IMO it's plausible that her husband simply lied).
I'm on the side of they are both evil. She has had no contact with the son, she herself adopted for years, she's never came by to visit, even if she didn't know about dad 2 kicking him out, she never followed up, she was like that all his life, cast to the sidelines.
Looks like they treat their own blood daughter not much better, no 18 birthday, to busy with their own drama to care for a child and truency for more than a year and nothing is done. Plenty of signs there both are sh**